Arthur Ashe Stadium debuted a brand new look, as the world’s largest tennis venue now has a retractable roof overhead.

Arthur Ashe Kids’ day brought fun for everyone as hundreds of children packed the site for games, music and tennis.

A pair of Olympic medalists were on hand to teach the kids some tennis, including Monica Puig and Venus Williams.

Gold and silver medalist swimmer Simone Manuel was also in attendance.

Meanwhile, Turkey’s Cagla Buyukakcay kicked off the first-round in historic fashion: besides grabbing her first win in her US Open main draw debut, she also recorded the first victory of the tournament.

A few minutes later, last year’s finalist Roberta Vinci recorded the tournament’s first win on Arthur Ashe Stadium.

Two-time finalist Caroline Wozniacki inaugurated the new Grandstand court with a three set battle.

Wozniacki came back from a set down against Taylor Townsend to advance to Round 2.

WTA Legend and two-time US Open champion Monica Seles also surprised fans at an on-site activity.

She answered lots of questions, as well as gave a few tennis tips.

As the sun set, the first night session of the US Open was inaugurated with a spectacular Opening Ceremony.

Phil Collins provided the night’s musical entertainment, along with Leslie Odom Jr.

And we finally got to see the roof in action. (Thankfully, there was no rain in sight, just lights!)

The roof was back open for Madison Keys and Alison Riske, who made history by finishing just shy of 2 a.m., the latest finish ever recorded in a women’s match.

The stars were out in full force at the US Open, including fashion icons like Vera Wang and Anna Wintour.

They packed the stands to see World No.1 Serena Williams begin her 2016 US Open campaign with a straight sets win over Ekaterina Makarova.